principe azul
Ian
Another issue is, that, on many M adapters, the lens is not aligned well at the 12 o'clock position (something which can be repaired, afaik, RFF member Ferider has posted a tutorial for that)
Easy fix. Unscrew and carefully remove the lensmount, and you'll see there are three closely-spaced holes underneath at each point where the screw was. Realign lensmount to holes that will let the ears of the hood sit correctly, and screw back in.